The long-term goal of this project is to study mechanisms of pituitary control of ovarian aging in women. Normal ovarian function is dependent on follicle-stimulating hormone (FSH), a pituitary derived heterodimeric glycoprotein consisting of an a and a p subunit. Both the subunits are glycosylated with two chains in each subunit. This common FSH form is called tetra-glycosylated FSH. Glycosylation plays a major role in secretion, serum half-life and biological actions of FSH. It is known that glycosylation of pituitary gonadotropins is also estrous/menstrual cycle- and age-specific. Biochemical and physiological studies have identified in several species a unique di-glycosylated variant consisting of sugar chains only in the a but not p subunits. Most importantly, the ratio of tetra- and di-glycosylated FSH is found to be age-dependant, with low levels of di-glycosylated variant predominantly present in post-menopausal women. However, the distinct in vivo biological functions of these FSH variants are unknown in normal ovarian physiology. The hypothesis is that a more potent di-glycosylated FSH is required for optimal stimulation of foliiculogenesis, but not in the aging ovary. This hypothesis will be tested in genetically engineered mouse models in three specific Aims. In Aim 1, we will test the in vivo potencies of biochemically purified FSH variants from different ages of women using FSHp knockout mice. In Aim 2, we will produce transgenic mice with a directed expression of this variant in gonadotropes and introduce this transgene into FSHp null genetic background, to test the biological actions of di-glycosylated variant. In Aim 3, we will temporally regulate the expression (gene switch) of the di-glycosylated FSH variant on a FSHp null background and identify the age-specific biological effects of di-glycosylated variant. Functional analyses with the above genetic models will identify distinct biological actions of FSH variants in vivo during ovarian aging. Ovarian follicle reserve diminishes with aging in women as well as other species and this directly affects the oocyte quality. Therefore, our studies will have a direct clinical impact in formulating new treatments for enhancing the production of healthy follicles and oocytes in aging women.